Clearly the outliers here are Alan Wake and Bioshock 2. The other games are slower paced, and they are more peaceful in general. For example Broken Sword is a point-and-click adventure game that I love, but it can be slow at times. I fell asleep playing it on my Nintendo DS while on a roadtrip - I dropped the stylus and woke up about 20 minutes later wondering if I was really enjoying the game as much as I thought I was.

For my part, current "nodding off" games include Skyrim, Persona 3, and Minecraft. I also have some strong memories of catching some zz's while playing Final Fantasy VII last year. However, I really like all of those games!

I think the science may be a little flawed on this (super scientific) study—or at least, sleep-inducingness shouldn't really be linked to how much you're enjoying a certain game. After all, the games that I'm likely to fall asleep playing are the ones that I play into the deep hours of the night. Those are the games I like most, else I wouldn't be playing them at 3AM.